Polyethylene compositions, process and closures

ABSTRACT

A dual reactor solution process gives high density polyethylene compositions containing a first ethylene copolymer and a second ethylene copolymer and which have good processability and ESCR properties. The polyethylene compositions are suitable for compression molding or injection molding applications and are particularly useful in the manufacture of caps and closures for bottles or containers.

The present disclosure relates to polyethylene compositions that areuseful in the manufacture of molded articles such as for exampleclosures for containers or bottles.

Polymer compositions useful for molding applications, such as caps andclosures for bottles are known. One-piece closures, such as screw capshave been made from high density polyethylene resins. The use of highdensity resin polyethylene is required to impart sufficient stiffness tothe closures, while broader molecular weight distributions are alsodesirable in order to provide good flow properties and to improveenvironmental stress crack resistance (ESCR).

Polyethylene blends produced with conventional Ziegler-Natta or Phillipstype catalysts systems can be made having suitably high density and ESCRproperties, see for example, WO 00/71615 and U.S. Pat. No. 5,981,664.However, the use of conventional catalyst systems typically producessignificant amounts of low molecular weight polymer chains having highcomonomer contents, which results in resins having non-idealorganoleptic properties.

Examples of high density multimodal polyethylene blends made usingconventional catalyst systems for the manufacture of caps or closuresare taught in U.S. Patent Nos 2005/0004315A1; 2005/0267249A1; as well asWO 2006/048253, WO 2006/048254, WO 2007/060007; and EP 2,017,302A1.Further high density, multimodal polyethylene blends made by employingconventional Ziegler-Natta catalysts are disclosed in U.S. Patent Nos.2009/0062463A1; 2009/0198018; 2009/0203848 and in WO 2007/130515, WO2008/136849 and WO 2010/088265.

In contrast to traditional catalysts, the use of so called single sitecatalysts (such as “metallocene” and “constrained geometry” catalysts)provides resin having lower catalyst residues and improved organolepticproperties as taught by U.S. Pat. No. 6,806,338. The disclosed resinsare suitable for use in molded articles. Further resins comprisingmetallocene catalyzed components and which are useful for moldingapplications are described in U.S. Pat. Nos. 7,022,770; 7,307,126;7,396,878 and 7,396,881 and 7,700,708.

U.S. Patent Application Publication No. 2011/0165357A1 discloses a blendof metallocene catalyzed resins which is suitable for use in pressureresistant pipe applications.

U.S. Patent Application Publication No. 2006/0241256A1 teaches blendsformulated from polyethylenes made using a hafnocene catalyst in theslurry phase.

A bimodal resin having a relatively narrow molecular weight distributionand long chain branching is described in U.S. Pat. No. 7,868,106. Theresin is made using a bis-indenyl type metallocene catalyst in a dualslurry loop polymerization process and can be used to manufacture capsand closures.

U.S. Pat. No. 6,642,313 discloses multimodal polyethylene resins whichare suitable for use in the manufacture of pipes. A dual reactorsolution process is used to prepare the resins in the presence of aphosphinimine catalyst.

Narrow molecular weight polyethylene blends comprising a metalloceneproduced polyethylene component and a Ziegler-Natta or metalloceneproduced polyethylene component are reported in U.S. Pat. No. 7,250,474.The blends can be used in blow molding and injection moldingapplications such as for example, milk bottles and bottle capsrespectively.

In U.S. Pat. No. 8,022,143 we disclosed a resin composition having agood balance of toughness, ESCR, processability, and organolepticproperties for use in the manufacture of caps and closures. The resinswere made using a single site catalyst system in a dual reactor solutionprocess, to provide bimodal polyethylene compositions in which comonomerwas present in both a high and a low molecular weight component. Thedisclosed resins had a normal comonomer distribution in that the lowmolecular weight component had a larger amount of comonomer than did thehigh molecular weight component. In U.S. Pat. No. 8,962,755 we disclosedthat by adding more comonomer to the high molecular weight component ofthese resins, we can improve the ESCR properties.

We now report a new polyethylene composition which is suitable formolding applications, with a good balance of ESCR and processability andwhich has improved melt strength.

The present disclosure provides a polyethylene composition that can beused in the manufacture of caps and closures.

Provided in one embodiment of the disclosure is a closure, the closurecomprising a bimodal polyethylene composition comprising: (1) 10 to 70wt % of a first ethylene copolymer having a melt index I₂, of less than0.4 g/10 nnin; a molecular weight distribution M_(w)/M_(n), of less than2.7; and a density of from 0.920 to 0.955 g/cm³; and (2) 90 to 30 wt %of a second ethylene copolymer having a melt index I₂, of from 250 to20,000 g/10 min; a molecular weight distribution M_(w)/M_(n), of lessthan 2.7; and a density higher than the density of the first ethylenecopolymer, but less than 0.965 g/cm³; wherein the density of the secondethylene copolymer is less than 0.035 g/cm³ higher than the density ofthe first ethylene copolymer; the ratio (SCB1/SCB2) of the number ofshort chain branches per thousand carbon atoms in the first ethylenecopolymer (SCB1) to the number of short chain branches per thousandcarbon atoms in the second ethylene copolymer (SCB2) is greater than1.0; and wherein the bimodal polyethylene composition has a molecularweight distribution M_(w)/M_(n), of from 5.0 to 13.0, a density of from0.949 to 0.958 g/cm³, a stress exponent of less than 1.53, a melt index(I₂) of from 0.3 to 3.0 g/10 min, and which satisfies the following:400,000≦Mz≦500,000.

Provided in one embodiment of the disclosure is a process to prepare apolyethylene composition, the polyethylene composition comprising: (1)10 to 70 wt % of a first ethylene copolymer having a melt index I₂, ofless than 0.4 g/10 min; a molecular weight distribution M_(w)/M_(n), ofless than 2.7; and a density of from 0.920 to 0.955 g/cm³; and (2) 90 to30 wt % of a second ethylene copolymer having a melt index I₂, of from250 to 20,000 g/10 min; a molecular weight distribution M_(w)/M_(n), ofless than 2.7; and a density higher than the density of the firstethylene copolymer, but less than 0.965 g/cm³; wherein the density ofthe second ethylene copolymer is less than 0.035 g/cm³ higher than thedensity of the first ethylene copolymer; the ratio (SCB1/SCB2) of thenumber of short chain branches per thousand carbon atoms in the firstethylene copolymer (SCB1) to the number of short chain branches perthousand carbon atoms in the second ethylene copolymer (SCB2) is greaterthan 1.0; and wherein the bimodal polyethylene composition has amolecular weight distribution M_(w)/M_(n), of from 5.0 to 13.0, adensity of from 0.949 to 0.958 g/cm³, a stress exponent of less than1.53, a melt index (I₂) of from 0.3 to 3.0 g/10 min, a broadness factordefined as (M_(w)/M_(n))/(M_(z)/M_(w)) of ≦2.75, and which satisfies thefollowing: 400,000≦Mz≦500,000; the process comprising contacting atleast one single site polymerization catalyst system with ethylene andat least one alpha-olefin under solution polymerization conditions in atleast two polymerization reactors.

Provided in one embodiment of the disclosure is a bimodal polyethylenecomposition comprising: (1) 10 to 70 wt % of a first ethylene copolymerhaving a melt index I₂, of less than 0.4 g/10 min; a molecular weightdistribution M_(w)/M_(n), of less than 2.7; and a density of from 0.920to 0.955 g/cm³; and (2) 90 to 30 wt % of a second ethylene copolymerhaving a melt index I₂, of from 250 to 20,000 g/10 min; a molecularweight distribution M_(w)/M_(n), of less than 2.7; and a density higherthan the density of the first ethylene copolymer, but less than 0.965g/cm³; wherein the density of the second ethylene copolymer is less than0.035 g/cm³ higher than the density of the first ethylene copolymer; theratio (SCB1/SCB2) of the number of short chain branches per thousandcarbon atoms in said first ethylene copolymer (SCB1) to the number ofshort chain branches per thousand carbon atoms in the second ethylenecopolymer (SCB2) is greater than 1.0; and wherein the bimodalpolyethylene composition has a molecular weight distributionM_(w)/M_(n), of from 5.0 to 13.0, a density of from 0.949 to 0.958g/cm³, a stress exponent of less than 1.53, a melt index (I₂) of from0.3 to 3.0 g/10 min, and which satisfies the following:400,000≦Mz≦500,000.

Provided in one embodiment of the disclosure is a bimodal polyethylenecomposition comprising: (1) 10 to 70 wt % of a first ethylene copolymerhaving a melt index I₂, of less than 0.4 g/10 min; a molecular weightdistribution M_(w)/M_(n), of less than 2.7; and a density of from 0.920to 0.940 g/cm³; and (2) 90 to 30 wt % of a second ethylene copolymerhaving a melt index I₂, of from 1000 to 20,000 g/10 min; a molecularweight distribution M_(w)/M_(n), of less than 2.7; and a density higherthan the density of the first ethylene copolymer, but less than 0.965g/cm³; wherein the density of the second ethylene copolymer is less than0.035 g/cm³ higher than the density of the first ethylene copolymer; theratio (SCB1/SCB2) of the number of short chain branches per thousandcarbon atoms in the first ethylene copolymer (SCB1) to the number ofshort chain branches per thousand carbon atoms in the second ethylenecopolymer (SCB2) is greater than 1.0; and wherein the bimodalpolyethylene composition has a molecular weight distributionM_(w)/M_(n), of from 6.0 to 12.0, a density of from 0.949 to 0.957g/cm³, a stress exponent of less than 1.50, a melt index (I₂) of from0.3 to 2.0 g/10 min, a Rosand melt strength of at least 3.0 cN, andwhich satisfies the following: 400,000≦Mz≦500,000.

In an embodiment of the disclosure, the bimodal polyethylene compositionhas an ESCR Condition B (10% IGEPAL) of at least 150 hrs.

In an embodiment of the disclosure, the bimodal polyethylene compositionhas a molecular weight distribution, M_(w)/M_(n), of from 6.0 to 11.0.

In an embodiment of the disclosure, the bimodal polyethylene compositionhas melt index I₂, of from 0.3 to less than 1.0 g/10 min.

In an embodiment of the disclosure, the bimodal polyethylene compositionhas a density of from 0.951 to 0.955 g/cm³.

In an embodiment of the disclosure, the bimodal polyethylene compositionhas a composition distribution breadth index (CDBI25) of greater than55% by weight.

In an embodiment of the disclosure, the bimodal polyethylene compositioncomprises: from 30 to 60 wt % of the first ethylene copolymer; and from70 to 40 wt % of the second ethylene copolymer.

In an embodiment of the disclosure, the bimodal polyethylene compositionhas a Rosand melt strength of at least 3.0 cN.

In an embodiment of the disclosure, the bimodal polyethylene compositionhas a broadness factor defined as (M_(w)/M_(n))/(M_(z)/M_(w)) of 5 2.75.

In an embodiment of the disclosure, the bimodal polyethylene compositionhas a shear viscosity ratio of ≧15.

In an embodiment of the disclosure, the bimodal polyethylene compositionfurther comprises a nucleating agent or a mixture of nucleating agents.

In an embodiment of the disclosure, the closure is made by compressionmolding or injection molding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plot of the ESCR in hours (the ESCR B10 for a moldedplaque) against the 2% secant flexural modulus (MPa) for selectedinventive and comparative polyethylene example compositions.

FIG. 2 shows a plot of the “the shear viscosity ratio” (η₁₀/η₁₀₀₀ at240° C.) against the ESCR in hours (the ESCR B10 for a molded plaque)for selected inventive and comparative polyethylene examples.

FIG. 3 shows a plot of the “the shear viscosity ratio” (η₁₀/η₁₀₀₀ at240° C.) against the Rosand melt strength (cN) for selected inventiveand comparative polyethylene examples.

FIG. 4 shows a gel permeation chromatograph for inventive polyethyleneexamples Nos 1, 2 and 3.

FIG. 5 shows the relationship between the shear thinning indexSHI_((1,100)) and the melt index, I₂ of polyethylene compositions of thecurrent disclosure.

DETAILED DESCRIPTION

The present disclosure is related to molded parts, such as closures forbottles/containers and the polyethylene compositions used to manufacturethem. The polyethylene compositions are composed of at least twoethylene copolymer components: a first ethylene copolymer and a secondethylene copolymer.

By the term “ethylene copolymer” it is meant that the copolymercomprises both ethylene and at least one alpha-olefin cornonomer.

The terms “cap” and “closure” are used interchangeably in the currentdisclosure, and both connote any suitably shaped molded article forenclosing, sealing, closing or covering etc., a suitably shaped opening,a suitably molded aperture, an open necked structure or the like used incombination with a container, a bottle, a jar and the like.

The terms “homogeneous” or “homogeneously branched polymer” as usedherein define homogeneously branched polyethylene which has a relativelynarrow composition distribution, as indicated by a relatively highcomposition distribution breadth index (CDBI₅₀). That is, the comonomeris randomly distributed within a given polymer chain and a substantialportion of the polymer chains have same ethylene/comonomer ratio. It iswell known that metallocene catalysts and other so called “single sitecatalysts” incorporate comonomer more evenly than traditionalZiegler-Natta catalysts when used for catalytic ethylenecopolymerization with alpha olefins. This fact is often demonstrated bymeasuring the composition distribution breadth index (CDBI₅₀) forcorresponding ethylene copolymers. The composition distribution of apolymer can be characterized by the short chain distribution index(SCDI) or composition distribution breadth index (CDBI₅₀). Thedefinition of composition distribution breadth index (CDBI₅₀) can befound in PCT publication WO 93/03093 and U.S. Pat. No. 5,206,075. TheCDBI₅₀ is conveniently determined using techniques which isolate polymerfractions based on their solubility (and hence their comonomer content).For example, temperature rising elution fractionation (TREF) asdescribed by Wild et al. J. Poly. Sci., Poly. Phys. Ed. Vol. 20, p 441,1982 or in U.S. Pat. No. 4,798,081 can be employed. From the weightfraction versus composition distribution curve, the CDBI₅₀ is determinedby establishing the weight percentage of a copolymer sample that has acomonomer content within 50% of the median comonomer content on eachside of the median. Generally, Ziegler-Natta catalysts produce ethylenecopolymers with a CDBI₅₀ of less than about 50 weight %, or less thanabout 55 weight %, consistent with a heterogeneously branched copolymer.In contrast, metallocenes and other single site catalysts will mostoften produce ethylene copolymers having a CDBI₅₀ of greater than about55 weight %, or greater than about 60 weight %, consistent with ahomogeneously branched copolymer.

The First Ethylene Copolymer

In an embodiment of the disclosure, the first ethylene copolymer of thepolyethylene composition has a density of from about 0.920 g/cm³ toabout 0.955 g/cm³; a melt index, I₂, of less than about 0.4 g/10 min; amolecular weight distribution, M_(w)/M_(n), of below about 2.7 and aweight average molecular weight, M_(w), that is greater than the M_(w)of the second ethylene copolymer.

In an embodiment of the disclosure the first ethylene copolymer is ahomogeneously branched copolymer.

In an embodiment of the disclosure, the first ethylene copolymer is madewith a single site catalyst, such as for example a phosphiniminecatalyst.

In an embodiment of the disclosure, the comonomer (i.e., alpha-olefin)content in the first ethylene copolymer can be from about 0.05 to about3.0 mol %. The comonomer content of the first ethylene copolymer may bedetermined by mathematical deconvolution methods as applied to a bimodalpolyethylene composition (see the Examples section).

In embodiments of the disclosure, the comonomer in the first ethylenecopolymer is one or more alpha olefin such as but not limited to1-butene, 1-hexene, 1-octene and the like.

In an embodiment of the disclosure, the first ethylene copolymer is acopolymer of ethylene and 1-octene.

In an embodiment of the disclosure, the short chain branching in thefirst ethylene copolymer can be from about 0.25 to about 15 short chainbranches per thousand carbon atoms (SCB1/1000Cs). In further embodimentsof the disclosure, the short chain branching in the first ethylenecopolymer can be from 0.5 to 15, or from 0.5 to 12, or from 0.5 to 10,or from 0.75 to 15, or from 0.75 to 12, or from 0.75 to 10, or from 1.0to 10, or from 1.0 to 8.0, or from 1.0 to 5, or from 1.0 to 3 branchesper thousand carbon atoms (SCB1/1000Cs). The short chain branching isthe branching due to the presence of alpha-olefin comonomer in theethylene copolymer and will for example have two carbon atoms for a1-butene comonomer, or four carbon atoms for a 1-hexene comonomer, orsix carbon atoms for a 1-octene comonomer, etc. The number of shortchain branches in the first ethylene copolymer may be determined bymathematical deconvolution methods as applied to a bimodal polyethylenecomposition (see the Examples section).

In an embodiment of the disclosure, the comonomer content in the firstethylene copolymer is greater than comonomer content of the secondethylene copolymer (as reported for example in mol %).

In an embodiment of the disclosure, the amount of short chain branchingin the first ethylene copolymer is greater than the amount of shortchain branching in the second ethylene copolymer (as reported in shortchain branches, SCB per thousand carbons in the polymer backbone,1000Cs).

The melt index, I₂ of the first ethylene copolymer can in an embodimentof the disclosure be above 0.01, but below 0.4 g/10 nnin. In furtherembodiments of the disclosure, the melt index, I₂ of the first ethylenecopolymer will be from 0.01 to 0.40 g/10 min, or from 0.01 to 0.30 g/10min, or from 0.01 to 0.25 g/10 min, or from 0.01 to 0.20 g/10 min, orfrom 0.01 to 0.10 g/10 min.

In an embodiment of the disclosure, the first ethylene copolymer has aweight average molecular weight M_(w) of from about 110,000 to about300,000 (g/mol). In another embodiment of the disclosure, the firstethylene copolymer has a weight average molecular weight M_(w) of fromabout 110,000 to about 275,000. In embodiments of the disclosure, thefirst ethylene copolymer has a weight average molecular weight M_(w) offrom about 125,000 to about 275,000, or from about 125,000 to about250,000, or from 125,000 to about 230,000, or from about 150,000 toabout 275,000, or from about 150,000 to about 250,000, or from about175,000 to about 250,000, or from about 180,000 to about 230,000. Inembodiments of the disclosure, the first ethylene copolymer has a M_(w)of greater than 150,000, or greater than 175,000, or greater than180,000, or greater than 190,000, or greater than 200,000. Inembodiments of the disclosure the first ethylene copolymer has a M_(w)of greater than 150,000, or greater than 175,000, or greater than180,000, or greater than 190,000, or greater than 200,000 while at thesame time being lower than 275,000, or 250,000.

In an embodiment of the disclosure, the density of the first ethylenecopolymer is from 0.920 to 0.955 g/cm³, including narrower ranges withinthis range and all the numbers encompassed by this range. For example,in further embodiments of the disclosure, the density of the firstethylene copolymer can be from 0.925 to 0.955 g/cm³, or from 0.925 to0.950 g/cm³, or from 0.925 to 0.945 g/cm³, or from 0.925 to 0.940 g/cm³,or from 0.920 to 0.940 g/cm³, or from 0.922 to 0.948 g/cm³, or from0.925 to 0.935 g/cm³, or from 0.927 to 0.945 g/cm³, or from 0.927 to0.940 g/cm³, or from 0.927 to 0.935 g/cm³.

In an embodiments of the disclosure, the first ethylene copolymer has amolecular weight distribution (M_(w)/M_(n)) of <3.0, or ≦2.7, or <2.7,or 23 2.5, or <2.5, or ≦2.3, or from 1.8 to 2.3.

The M_(w)/M_(n) value of the first ethylene copolymer can in anembodiment of the disclosure be estimated by a de-covolution of a GPCprofile obtained for a bimodal polyethylene composition of which thefirst ethylene copolymer is a component.

The density and the melt index, I₂, of the first ethylene copolymer canbe estimated from GPC (gel permeation chromatography) and GPC-FTIR (gelpermeation chromatography with Fourier transform infra-red detection)experiments and deconvolutions carried out on the bimodal polyethylenecomposition (see the Examples section).

In an embodiment of the disclosure, the first ethylene copolymer of thepolyethylene composition is a homogeneously branched ethylene copolymerhaving a weight average molecular weight, Mw, of at least 175,000; amolecular weight distribution, M_(w)/M_(n), of less than 2.7 and adensity of from 0.922 to 0.948 g/cm³.

In an embodiment of the present disclosure, the first ethylene copolymeris homogeneously branched ethylene copolymer and has a CDBI₅₀ of greaterthan about 60 weight %. In further embodiments of the disclosure, thefirst ethylene copolymer has a CDBI₅₀ of greater than about 65 weight %,or greater than about 70 weight %, or greater than about 75 weight %, orgreater than about 80 weight %.

In an embodiment of the disclosure, the first ethylene copolymercomprises from 10 to 70 weight percent (wt %) of the total weight of thefirst and second ethylene copolymers. In an embodiment of thedisclosure, the first ethylene copolymer comprises from 20 to 60 weightpercent (wt %) of the total weight of the first and second ethylenecopolymers. In an embodiment of the disclosure, the first ethylenecopolymer comprises from 30 to 60 weight percent (wt %) of the totalweight of the first and second ethylene copolymers. In an embodiment ofthe disclosure, the first ethylene copolymer comprises from 40 to 50weight percent (wt %) of the total weight of the first and secondethylene copolymers.

The Second Ethylene Copolymer

In an embodiment of the disclosure, the second ethylene copolymer of thepolyethylene composition has a density below 0.965 g/cm³ but which ishigher than the density of the first ethylene copolymer; a melt index,I₂, of from about 250 to 20,000 g/10 min; a molecular weightdistribution, M_(w)/M_(n), of below about 2.7 and a weight averagemolecular weight M_(w) that is less than the M_(w) of the first ethylenecopolymer.

In an embodiment of the disclosure, the second ethylene copolymer ishomogeneously branched copolymer.

In an embodiment of the disclosure, the second ethylene copolymer ismade with a single site catalyst, such as for example a phosphiniminecatalyst.

In an embodiment of the disclosure, the comonomer content in the secondethylene copolymer can be from about 0.01 to about 3 mol % or from about0.03 to about 3 mol %, or from about 0.05 to about 3 mol % as measuredby ¹³C NMR, or FTIR or GPC-FTIR methods. The comonomer content of thesecond ethylene polymer may be determined by mathematical deconvolutionmethods applied to a bimodal polyethylene composition (see the Examplessection).

In an embodiment of the disclosure, the comonomer in the second ethylenecopolymer is one or more alpha olefin such as but not limited to1-butene, 1-hexene, 1-octene and the like.

In an embodiment of the disclosure, the second ethylene copolymer is acopolymer of ethylene and 1-octene.

In an embodiment of the disclosure, the short chain branching in thesecond ethylene copolymer can be from about 0.15 to about 15 short chainbranches per thousand carbon atoms (SCB2/1000Cs). In further embodimentsof the disclosure, the short chain branching in the second ethylenecopolymer can be from 0.15 to 12, or from 0.15 to 8, or from 0.15 to 5,or from 0.15 to 3, or from 0.15 to 2 branches per thousand carbon atoms(SCB2/1000Cs). The short chain branching is the branching due to thepresence of alpha-olefin comonomer in the ethylene copolymer and willfor example have two carbon atoms for a 1-butene comonomer, or fourcarbon atoms for a 1-hexene comonomer, or six carbon atoms for a1-octene comonomer, etc.

The number of short chain branches in the second ethylene copolymer maybe determined by mathematical deconvolution methods applied to a bimodalpolyethylene composition (see the Examples section).

In an embodiment of the disclosure, the short chain branching in thesecond ethylene copolymer can be from about 0.05 to about 10 short chainbranches per thousand carbon atoms (SCB1/1000Cs). In further embodimentsof the disclosure, the short chain branching in the second copolymer canbe from 0.05 to 7.5, or from 0.05 to 5.0, or from 0.05 to 2.5, or from0.05 to 1.5, or from 0.1 to 12, or from 0.1 to 10, or from 0.1 to 7.5,or from 0.1 to 5.0, or from 0.1 to 2.5, or from 0.1 to 2.0, or from 0.1to 1.0 branches per thousand carbon atoms (SCB1/1000Cs).

In an embodiment of the disclosure, the comonomer content in the secondethylene copolymer is less than the comonomer content of the firstethylene copolymer (as reported for example in mol %).

In an embodiment of the disclosure, the amount of short chain branchingin the second ethylene copolymer is less than the amount of short chainbranching in the first ethylene copolymer (as reported in short chainbranches, SCB per thousand carbons in the polymer backbone, 1000Cs).

In an embodiment of the present disclosure, the density of the secondethylene copolymer is less than 0.967 g/cm³. The density of the secondethylene copolymer in another embodiment of the disclosure is less than0.966 g/cm³. In another embodiment of the disclosure, the density of thesecond ethylene copolymer is less than 0.965 g/cm³. In anotherembodiment of the disclosure, the density of the second ethylenecopolymer is less than 0.964 g/cm³. In another embodiment of thedisclosure, the density of the second ethylene copolymer is less than0.963 g/cm³. In another embodiment of the disclosure, the density of thesecond ethylene copolymer is less than 0.962 g/cm³.

In an embodiment of the present disclosure, the density of the secondethylene copolymer is higher than the density of the first ethylenecopolymer, but is less than 0.967 g/cm³. The density of the secondethylene copolymer in another embodiment of the disclosure is higherthan the density of the first ethylene copolymer, but is less than 0.966g/cm³. In another embodiment of the disclosure, the density of thesecond ethylene copolymer is higher than the density of the firstethylene copolymer, but is less than 0.965 g/cm³. In another embodimentof the disclosure, the density of the second ethylene copolymer ishigher than the density of the first ethylene copolymer, but is lessthan 0.964 g/cm³. In another embodiment of the disclosure, the densityof the second ethylene copolymer is higher than the density of the firstethylene copolymer, but is less than 0.963 g/cm³. In another embodimentof the disclosure, the density of the second ethylene copolymer ishigher than the density of the first ethylene copolymer, but is lessthan 0.962 g/cm³.

In embodiments of the disclosure, the density of the second ethylenecopolymer is from 0.952 to 0.966 g/cm³ including narrower ranges withinthis range and all the numbers within this range, such as, for example,from 0.952 to 0.965 g/cm³, or from 0.952 to 0.964 g/cm³, or from 0.952to 0.963 g/cm³, or from 0.954 to 0.963 g/cm³, or from 0.954 to 0.964g/cm³, or from 0.956 to 0.963 g/cm³.

In embodiments of the disclosure, the second ethylene copolymer has aweight average molecular weight M_(w) of less than about 45,000, or lessthan about 40,000 or less than about 35,000. In another embodiment ofthe disclosure, the second ethylene copolymer has a weight averagemolecular weight M_(w) of from about 7,500 to about 35,000. In furtherembodiments of the disclosure, the second ethylene copolymer has aweight average molecular weight M_(w) of from about 9,000 to about35,000, or from about 10,000 to about 35,000, or from about 12,500 toabout 30,000, or from about 10,000 to about 25,000, or from about 10,000to about 20,000.

In some embodiments of the disclosure, the second ethylene copolymer hasa molecular weight distribution (Mw/Mn) of <3.0, or ≦2.7, or <2.7, or≦2.5, or <2.5, or ≦2.3, or from 1.8 to 2.3.

The Mw/Mn value of the second ethylene copolymer can in an embodiment ofthe disclosure be estimated by a de-covolution of a GPC profile obtainedfor a bimodal polyethylene composition of which the first ethylenecopolymer is a component.

In an embodiment of the disclosure, the melt index I₂ of the secondethylene copolymer can be from 50 to 20,000 g/10 min. In anotherembodiment of the disclosure, the melt index I₂ of the second ethylenecopolymer can be from 250 to 20,000 g/10 min. In another embodiment ofthe disclosure, the melt index I₂ of the second ethylene copolymer canbe from 500 to 20,000 g/10 min. In another embodiment of the disclosure,the melt index I₂ of the second ethylene copolymer can be from 1000 to20,000 g/10 min. In yet another embodiment of the disclosure, the meltindex I₂ of the second ethylene copolymer can be from 1500 to 20,000g/10 min. In yet another embodiment of the disclosure, the melt index I₂of the second ethylene copolymer can be from 1500 to 10,000 g/10 min. Inyet another embodiment of the disclosure, the melt index I₂ of thesecond ethylene copolymer can be from 1500 to 7,000 g/10 min. In yetanother embodiment of the disclosure, the melt index I₂ of the secondethylene copolymer can be greater than 1500, but less than 7000 g/10min. In yet another embodiment of the disclosure, the melt index I₂ ofthe second ethylene copolymer can be greater than 1500, but less than5000 g/10 min. In yet another embodiment of the disclosure, the meltindex I₂ of the second ethylene copolymer can be greater than 1000, butless than 3500 g/10 min.

In an embodiment of the disclosure, the melt index I₂ of the secondethylene copolymer is greater than 200 g/10 min. In an embodiment of thedisclosure, the melt index I₂ of the second ethylene copolymer isgreater than 500 g/10 min. In an embodiment of the disclosure, the meltindex I₂ of the second ethylene copolymer is greater than 1000 g/10 min.In an embodiment of the disclosure, the melt index I₂ of the secondethylene copolymer is greater than 1500 g/10 min. In an embodiment ofthe disclosure, the melt index I₂ of the second ethylene copolymer isgreater than 1750 g/10 min.

The density and the melt index, I₂, of the second ethylene copolymer canbe estimated from GPC and GPC-FTIR experiments and deconvolutionscarried out on a bimodal polyethylene composition (see the belowExamples section).

In an embodiment of the disclosure, the second ethylene copolymer of thepolyethylene composition is a homogeneous ethylene copolymer having aweight average molecular weight, Mw, of at most 45,000; a molecularweight distribution, M_(w)/M_(n), of less than 2.7 and a density higherthan the density of the first ethylene copolymer, but less than 0.965g/cm³.

In an embodiment of the present disclosure, the second ethylenecopolymer is homogeneously branched ethylene copolymer and has a CDBI₅₀of greater than about 60 weight %. In further embodiments of thedisclosure, the second ethylene copolymer has a CDBI₅₀ of greater thanabout 65 weight %, or greater than about 70 weight %, or greater thanabout 75 weight %, or greater than about 80 weight %.

In an embodiment of the disclosure, the second ethylene copolymercomprises from 90 to 30 wt % of the total weight of the first and secondethylene copolymers. In an embodiment of the disclosure, the secondethylene copolymer comprises from 80 to 40 wt % of the total weight ofthe first and second ethylene copolymers. In an embodiment of thedisclosure, the second ethylene copolymer comprises from 70 to 40 wt %of the total weight of the first and second ethylene copolymers. In anembodiment of the disclosure, the second ethylene copolymer comprisesfrom 60 to 50 wt % of the total weight of the first and second ethylenecopolymers.

In the present disclosure, the second ethylene copolymer has a densitywhich is higher than the density of the first ethylene copolymer, butless than about 0.037 g/cm³ higher than the density of the firstethylene copolymer. In an embodiment of the disclosure, the secondethylene copolymer has a density which is higher than the density of thefirst ethylene copolymer, but less than about 0.035 g/cm³ higher thanthe density of the first ethylene copolymer. In another embodiment ofthe disclosure, the second ethylene copolymer has a density which ishigher than the density of the first ethylene copolymer, but less thanabout 0.033 g/cm³ higher than the density of the first ethylenecopolymer. In another embodiment of the disclosure, the second ethylenecopolymer has a density which is higher than the density of the firstethylene copolymer, but less than about 0.032 g/cm³ higher than thedensity of the first ethylene copolymer. In still another embodiment ofthe disclosure, the second ethylene copolymer has a density which ishigher than the density of the first ethylene copolymer, but less thanabout 0.031 g/cm³ higher than the density of the first ethylenecopolymer. In still another embodiment of the disclosure, the secondethylene copolymer has a density which is higher than the density of thefirst ethylene copolymer, but less than about 0.030 g/cm³ higher thanthe density of the first ethylene copolymer.

In embodiments of the disclosure, the I₂ of the second ethylenecopolymer is at least 100 times, or at least 1000 times, or at least10,000 times, or at least 50,000 times the I₂ of the first ethylenecopolymer.

The Polyethylene Composition

Minimally, the polyethylene composition will contain a first ethylenecopolymer (as defined above) and a second ethylene copolymer (as definedabove) which are of different weight average molecular weight (M_(w))and/or melt index, I₂.

In embodiments of the disclosure, the polyethylene composition has abroad, bimodal or multimodal molecular weight distribution.

In an embodiment of the disclosure, the polyethylene composition willminimally comprise a first ethylene copolymer (as defined above) and asecond ethylene copolymer (as defined above) and the ratio (SCB1/SCB2)of the number of short chain branches per thousand carbon atoms in thefirst ethylene copolymer (i.e., SCB1) to the number of short chainbranches per thousand carbon atoms in the second ethylene copolymer(i.e., SCB2) will be greater than 1.0 (i.e., SCB1/SCB2>1.0).

In an embodiment of the disclosure, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) is at least 1.0. Inyet another embodiment of the disclosure, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) is at least 1.25. Inanother embodiment of the disclosure, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) is at least 1.5. Inanother embodiment of the disclosure, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) is at least 1.75 or2.0 or 2.5.

In an embodiment of the disclosure, the ratio of the short chainbranching in the first ethylene copolymer (SCB1) to the short chainbranching in the second ethylene copolymer (SCB2) will be from greaterthan 1.0 to about 5.0, or from greater than 1.0 to about 4.0, or fromgreater than 1.0 to about 3.5.

In embodiments of the disclosure, the ratio (SCB1/SCB2) of the shortchain branching in the first ethylene copolymer (SCB1) to the shortchain branching in the second ethylene copolymer (SCB2) will be from 1.0to 12.0, or from 1.0 to 10, or from 1.0 to 7.0, or from 1.0 to 5.0, orfrom 1.0 to 3.0.

In an embodiment of the disclosure, the polyethylene composition has abimodal molecular weight distribution. In the current disclosure, theterm “bimodal” means that the polyethylene composition comprises atleast two components, one of which has a lower weight average molecularweight and a higher density and another of which has a higher weightaverage molecular weight and a lower density. A bimodal or multimodalpolyethylene composition may be identified by using gel permeationchromatography (GPC). Generally, the GPC chromatograph will exhibit twoor more component ethylene copolymers, where the number of componentethylene copolymers corresponds to the number of discernible peaks. Oneor more component ethylene copolymers may also exist as a hump, shoulderor tail relative to the molecular weight distribution of the otherethylene copolymer component.

In an embodiment of the disclosure, the polyethylene composition has adensity of greater than or equal to 0.949 g/cm³, as measured accordingto ASTM D792; a melt index, I₂, of from about 0.3 to about 4.0 g/10 min,as measured according to ASTM D1238 (when conducted at 190° C., using a2.16 kg weight); a molecular weight distribution, M_(w)/M_(n), of fromabout 5.0 to about 13.0, a Z-average molecular weight, M_(z) of from400,000 to 520,000, a stress exponent of less than 1.53 and anenvironmental stress crack resistance, ESCR Condition B at 10% of atleast 120 hours.

In embodiments of the disclosure, the polyethylene composition has acomonomer content of less than 0.75 mol %, or less than 0.70 mol %, orless than 0.65 mol %, or less than 0.60 mol %, or less than 0.55 mol %as measured by FTIR or ¹³C NMR methods, where the comonomer is one ormore alpha olefins such as but not limited to 1-butene, 1-hexene,1-octene and the like. In an embodiment of the disclosure, thepolyethylene composition has a comonomer content of from 0.1 to 0.75 mol%, or from 0.20 to 0.55 mol %, or from 0.25 to 0.50 mol %.

In embodiment of the present disclosure, the polyethylene compositionhas a density of at least 0.949 g/cm³. In further embodiments of thedisclosure, the polyethylene composition has a density of >0.949 g/cm³,or ≧0.950 g/cm³, or >0.950 g/cm³.

In an embodiment of the current disclosure, the polyethylene compositionhas a density in the range of from 0.949 to 0.960 g/cm³.

In an embodiment of the current disclosure, the polyethylene compositionhas a density in the range of from 0.949 to 0.959 g/cm³.

In an embodiment of the current disclosure, the polyethylene compositionhas a density in the range of from 0.949 to 0.958 g/cm³.

In an embodiment of the current disclosure, the polyethylene compositionhas a density in the range of from 0.949 to 0.957 g/cm³.

In an embodiment of the current disclosure, the polyethylene compositionhas a density in the range of from 0.949 to 0.956 g/cm³.

In an embodiment of the current disclosure, the polyethylene compositionhas a density in the range of from 0.949 to 0.955 g/cm³.

In an embodiment of the current disclosure, the polyethylene compositionhas a density in the range of from 0.950 to 0.955 g/cm³.

In an embodiment of the current disclosure, the polyethylene compositionhas a density in the range of from 0.951 to 0.957 g/cm³.

In an embodiment of the current disclosure, the polyethylene compositionhas a density in the range of from 0.951 to 0.955 g/cm³.

In an embodiment of the disclosure, the polyethylene composition has amelt index, I₂, of from 0.1 to 5.0 g/10 min according to ASTM D1238(when conducted at 190° C., using a 2.16 kg weight) including narrowerranges within this range and all the numbers within this range. Forexample, in further embodiments of the disclosure, the polyethylenecomposition has a melt index, I₂, of from 0.3 to 4.0 g/10 min, or from0.4 to 3.5 g/10 min, or from 0.4 to 3.0 g/10 min, or from 0.3 to 3.5g/10 min, or from 0.3 to 3.0 g/10 min, or from 0.3 to 2.5 g/10 min, orfrom 0.1 to 4.0 g/10 min, or from 0.1 to 3.5 g/10 min, or from 0.1 to3.0 g/10 min, or from 0.1 to 2.5 g/10 min, or from 0.1 to 2.0 g/10 min,or from 0.1 to 1.5 g/10 min, or from 0.25 to 1.5 g/10 min, or from 0.3to 2.0 g/10 min, or from 0.3 to 1.5 g/10 min, or less than 1.0 g/10 min,or from greater than 0.1 to less than 1.0 g/10 min, or from greater than0.2 to less than 1.0 g/10 min, or from greater than 0.3 to less than 1.0g/10 min.

In an embodiment of the disclosure, the polyethylene composition has amelt index I₅ of at least 1.0 g/10 min according to ASTM D1238 (whenconducted at 190° C., using a 5 kg weight). In another embodiment of thedisclosure, the polyethylene composition has a melt index, I₅, ofgreater than about 1.1 g/10 min, as measured according to ASTM D1238(when conducted at 190° C., using a 5 kg weight). In still furtherembodiments of the disclosure, the polyethylene composition has a meltindex I₅ of from about 1.0 to about 5.0 g/10 min, or from about 1.5 toabout 5.0 g/10 min, or from about 2.0 to about 5.0 g/10 min, or fromabout 2.0 to about 4.5 g/10 min.

In an embodiment of the disclosure, the polyethylene composition has ahigh load melt index, I₂₁ of at least 25 g/10 min according to ASTMD1238 (when conducted at 190° C., using a 21 kg weight). In anotherembodiment of the disclosure, the polyethylene composition has a highload melt index, I₂₁, of greater than about 50 g/10 min. In yet anotherembodiment of the disclosure, the polyethylene composition has a highload melt index, I₂₁, of greater than about 65 g/10 min.

In an embodiment of the disclosure, the ratio of the melt index, I₂, ofthe second ethylene copolymer to the melt index, I₅, of the polyethylenecomposition is from 200 to 2000. In another embodiment of thedisclosure, the ratio of the melt index, I₂, of the second ethylenecopolymer to the melt index, I₅, of the polyethylene composition is from400 to 1300. In yet another embodiment of the disclosure, the ratio ofthe melt index, I₂, of the second ethylene copolymer to the melt index,I₅, of the polyethylene composition is from 600 to 1200.

In an embodiment of the disclosure, the polyethylene composition has acomplex viscosity, η* at a shear stress (G*) anywhere between from about1 to about 10 kPa which is between 1,000 to 25,000 Pa·s. In anembodiment of the disclosure, the polyethylene composition has a complexviscosity, η* at a shear stress (G*) anywhere from about 1 to about 10kPa which is between 1,000 and 15,000, or from 5000 to 15,000.

In an embodiment of the disclosure, the polyethylene composition has anumber average molecular weight, M_(n), of below about 30,000. Infurther embodiments of the disclosure, the polyethylene composition hasa number average molecular weight, M_(n), of below about 20,000 or belowabout 17,500. In further embodiments of the disclosure, the polyethylenecomposition has a number average molecular weight, M_(n), of from about9,000 to 28,000, or from about 10,000 to 25,000, or from about 10,000 toabout 20,000.

In embodiments of the disclosure, the polyethylene composition has aweight average molecular weight, M_(w), of from about 65,000 to about200,000 including narrower ranges within this range and the numberswithin this range. For example, in further embodiments of thedisclosure, the polyethylene composition has a weight average molecularweight, M_(w), of from about 75,000 to about 175,000, or from about90,000 to about 150,000, or from about 100,000 to about 140,000.

In embodiments of the disclosure, the polyethylene composition has az-average molecular weight, M_(z), of from 400,000 to 520,000 includingnarrower ranges within this range and the numbers within this range. Forexample, in further embodiments of the disclosure, the polyethylenecomposition has a z-average molecular weight, M_(z), of from 400,000 to510,000, or from 400,000 to 500,000, or from 400,000 to 490,000, or from410,000 to 480,000.

In embodiments of the disclosure, the polyethylene composition has az-average molecular weight, M_(z) which satisfies: 400,000<Mz<500,000 or400,000≦Mz≦5 500,000.

In embodiments of the present disclosure, the polyethylene compositionhas a molecular weight distribution Mw/Mn of from 3.0 to 13.0, includingnarrower ranges within this range and all the numbers within this range.For example, in further embodiments of the disclosure, the polyethylenecomposition has a M_(w)/M_(n) of from 5.0 to 13.0, or from 4.0 to 12.0,or from 5.0 to 12.0 or from 6.0 to 12.0, or from 6.0 to 11.0, or from5.0 to 12.0, or from 5.0 to 10.0, or from 6.0 to 10.0, or from 6.0 to11.0, or from 7.0 to 11.0, or from greater than 7.0 to 11.0, or from 7.0to 10.0, or from greater than 7.0 to 12.0.

In embodiments of the disclosure, the polyethylene composition has aratio of Z-average molecular weight to weight average molecular weight(M_(z)/Mw) of from 2.25 to 5.0, or from 2.5 to 4.5, or from 2.75 to 5.0,or from 2.75 to 4.25, or from 3.0 to 4.0.

In an embodiment of the disclosure, the polyethylene composition has abroadness factor defined as (M_(w)/M_(n))/(M_(z)/M_(w)) of less than3.00, or less than 2.95, or less than 2.90, or less than 2.85, or lessthan 2.80, or less than 2.75, or less than 2.70, or less than 2.65, orless than 2.60, or less than 2.55, or less than 2.50, or less than 2.45,or less than 2.40, or less than 2.35, or ≦2.75, or ≦2.70, or ≦2.65, or≦2.60, or ≦2.55, or ≦2.50, or ≦2.45, or ≦2.40, or ≦2.35.

In embodiments of the disclosure, the polyethylene composition has amelt flow ratio defined as I₂₁/I₁₂ of >40, or ≧45, or ≧50, or ≧55, or≧60, or ≧65, or ≧70. In a further embodiment of the disclosure, thepolyethylene composition has a melt flow ratio I₂₁/I₂ of from about 40to about 120, including narrower ranges within this range and all thenumbers within this range. For example, the polyethylene composition mayhave a melt flow ratio I₂₁/I₂ of from about 50 to about 120, or fromabout 40 to about 110, or from about 45 to about 100, or from about 50to about 110, or from about 55 to about 95.

In an embodiment of the disclosure, the polyethylene composition has amelt flow rate defined as I₂₁/I₅ of less than 35. In another embodimentof the disclosure, the polyethylene composition has a melt flow ratedefined as I₂₁/I₅ of less than 30.

In an embodiment of the disclosure, the polyethylene composition has ashear viscosity at about 10⁵s⁻¹ (240° C.) of less than about 10 (Pa·s).In further embodiments of the disclosure, the polyethylene compositionhas a shear viscosity at about 10⁵s⁻¹ (240° C.) of less than 7.5 Pa·s,or less than 7.0 Pa·s, or less than 6.5 Pa·s.

In an embodiment of the disclosure, the polyethylene composition has ahexane extractables level of below 0.55 wt %.

In an embodiment of the disclosure, the polyethylene composition has atleast one type of alpha-olefin that has at least 4 carbon atoms and itscontent is less than 0.75 mol % as determined by ¹³C NMR. In anembodiment of the disclosure, the polyethylene composition has at leastone type of alpha-olefin that has at least 4 carbon atoms and itscontent is less than 0.65 mol % as determined by ¹³C NMR. In anembodiment of the disclosure, the polyethylene composition has at leastone type of alpha-olefin that has at least 4 carbon atoms and itscontent is less than 0.55 mol % as determined by ¹³C NMR.

In an embodiment of the disclosure, the shear viscosity ratio,SVR(_(10,000)) at 240° C. of the polyethylene composition can be fromabout 10 to 30, or from 12 to 27, or from 12.5 to 25, or from 15 to 25,or from 17.5 to 23.0. The shear viscosity ratio SVR(_(10,000)) isdetermined by taking the ratio of shear viscosity at shear rate of 10s⁻¹ and shear viscosity at shear rate of 1000 s⁻¹ as measured with acapillary rheometer at a constant temperature (e.g., 240° C.), and a diewith L/D ratio of 20 and diameter of 0.06″. Without wishing to be boundby theory, the higher the value for the shear viscosity ratio, theeasier the polyethylene composition is to be processed on convertingequipment for caps and closures. The “shear viscosity ratio” is usedherein as a means to describe the relative processability of apolyethylene composition.

In an embodiment of the disclosure, the polyethylene composition has ashear viscosity ratio (η₁₀/η₁₀₀₀ at 240° C.) of ≧12.0, ≧12.5, or ≧13.0,or ≧13.5, or ≧14.0, or ≧14.5, or ≧15.0, or ≧17.5, or ≧20.0.

In an embodiment of the disclosure, the shear thinning index,SHI(_(1,100)) of the polyethylene composition is less than about 10. Theshear thinning index (SHI), was calculated using dynamic mechanicalanalysis (DMA) frequency sweep methods as disclosed in PCT applicationsWO 2006/048253 and WO 2006/048254. The SHI value is obtained bycalculating the complex viscosities η*(1) and η*(100) at a constantshear stress of 1 kPa (G*) and 100 kPa (G*), respectively.

In an embodiment of the disclosure, the SHI(_(1,100)) of thepolyethylene composition satisfies the equation: SHI(_(1,100))<−10.58(log I₂ of polyethylene composition in g/10 min)/(g/10 min)+12.94. Inanother embodiment of the disclosure, the SHI(_(1,100)) of thepolyethylene composition satisfies the equation: SHI(_(1,100))<−5.5 (logI₂ of the polyethylene composition in g/10 min)/(g/10 min)+9.66.

In an embodiment of the disclosure, the polyethylene composition has aRosand melt strength in centiNewtons (cN) of at least 2.0, or at least2.25, or at least 2.5, or at least 2.75, or at least 3.0, or at least3.25, or at least 3.5, or at least 3.75, or from 2.5 to 6.0, or from2.75 to 6.0, or from 2.75 to 5.5, or from 3.0 to 6.0, or from 3.0 to5.5, or from 3.25 to 6.0, or from 3.5 to 6.0, or from 3.25 to 5.5.

In an embodiment of the disclosure, the polyethylene composition or amolded article (or plaque) made from the polyethylene composition, hasan environment stress crack resistance ESCR Condition B at 10% of atleast 50 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50°C. under condition B).

In an embodiment of the disclosure, the polyethylene composition or amolded article (or plaque) made from the polyethylene composition, hasan environment stress crack resistance ESCR Condition B at 10% of atleast 100 hrs, as measured according to ASTM D1693 (at 10% Igepal and50° C. under condition B).

In an embodiment of the disclosure, the polyethylene composition or amolded article (or plaque) made from the polyethylene composition, hasan environment stress crack resistance ESCR Condition B at 10% of atleast 150 hrs, as measured according to ASTM D1693 (at 10% Igepal and50° C. under condition B).

In an embodiment of the disclosure, the polyethylene composition or amolded article (or plaque) made from the polyethylene composition, hasan environment stress crack resistance ESCR Condition B at 10% of atleast 200 hrs, as measured according to ASTM D1693 (at 10% Igepal and50° C. under condition B).

In an embodiment of the disclosure, the polyethylene composition or amolded article (or plaque) made from the polyethylene composition, hasan environment stress crack resistance ESCR Condition B at 10% of from50 to 600 hrs, as measured according to ASTM D1693 (at 10% Igepal and50° C. under condition B).

In an embodiment of the disclosure, the polyethylene composition or amolded article (or plaque) made from the polyethylene composition, hasan environment stress crack resistance ESCR Condition B at 10% of from100 to 500 hrs, as measured according to ASTM D1693 (at 10% Igepal and50° C. under condition B).

In an embodiment of the disclosure, the polyethylene composition or amolded article (or plaque) made from the polyethylene composition, hasan environment stress crack resistance ESCR Condition B at 10% of from150 to 500 hrs, as measured according to ASTM D1693 (at 10% Igepal and50° C. under condition B).

In an embodiment of the disclosure, the polyethylene composition or amolded article (or plaque) made from the polyethylene composition has anotched Izod impact strength of at least 60 J/m, or at least 80 J/m asmeasured according to ASTM D256.

In an embodiment of the disclosure the polyethylene composition of thecurrent disclosure has a density of from 0.949 to 0.957 g/cm³; a meltindex, I₂, of from 0.3 to 2.0 g/10 min; a molecular weight distributionof from 6.0 to 12.0; a number average molecular weight, M_(n), of below30,000; a shear viscosity at 10⁵s⁻¹ (240° C.) of less than 10 (Pa·s), ahexane extractables of less than 0.55%, a notched Izod impact strengthof more than 60 J/m, and an ESCR B at 10% of at least 150 hrs.

In embodiments of the disclosure, the polyethylene composition has a 2%secant flexural modulus in megapascals (MPa) of greater than about 750,or greater than about 850, or greater than about 1000, or from about 750to about 1600, or from about 750 to about 1250, or from about 850 toabout 1150. In some embodiments, the polyethylene composition furthercomprises a nucleating agent which increases the 2% secant flexuralmodulus in megapascals (MPa) to above these ranges to for example frommore than about 1000 and up to about 1600. Without wishing to be boundby theory, the 2% secant flexural modulus is a measure of polymerstiffness. The higher the 2% secant flexural modulus, the higher thepolymer stiffness.

In an embodiment of the disclosure, the polyethylene composition has astress exponent, defined as Log₁₀[I₆/I₂]/Log₁₀[6.48/2.16], which is≦1.53. In further embodiments of the disclosure the polyethylenecomposition has a stress exponent, Log₁₀[I₆/I₂]/Log₁₀[6.48/2.16] of lessthan 1.50, or less than 1.48, or less than 1.45.

In an embodiment of the disclosure, the polyethylene composition has acomposition distribution breadth index (CDBI₅₀), as determined bytemperature elution fractionation (TREF), of ≧60 weight %. In furtherembodiments of the disclosure, the polyethylene composition will have aCDBI₅₀ of greater than 65 weight %, or greater than 70 weight %, orgreater than 75 weight %, or greater than 80 weight %.

In an embodiment of the disclosure, the polyethylene composition has acomposition distribution breadth index (CDBI₂₅), as determined bytemperature elution fractionation (TREF), of ≧50 weight %. In furtherembodiments of the disclosure, the polyethylene composition will have aCDBI₂₅ of greater than 55 weight %, or greater than 60 weight %, orgreater than 65 weight %, or greater than 70 weight %.

The polyethylene composition of this disclosure can be made using anyconventional blending method such as but not limited to physicalblending and in-situ blending by polymerization in multi reactorsystems. For example, it is possible to perform the mixing of the firstethylene copolymer with the second ethylene copolymer by molten mixingof the two preformed polymers. In some embodiments, preferred areprocesses in which the first and second ethylene copolymers are preparedin at least two sequential polymerization stages, however, bothin-series, or an in-parallel dual reactor process are contemplated foruse in the current disclosure. If the at least two reactors areconfigured in parallel, comonomer addition to each reactor makes anethylene copolymer in each reactor. If the at least two reactors areconfigured in series, comonomer may be added to at least the firstreactor, and unreacted comonomer can flow into later reactors to make anethylene copolymer in each reactor. Alternatively, if the at least tworeactors are configured in series, comonomer may be added to eachreactor, to make an ethylene copolymer in each reactor. Gas phase,slurry phase or solution phase reactor systems may be used, withsolution phase reactor systems being preferred in some embodiments.

In an embodiment of the current disclosure, a dual reactor solutionprocess is used as has been described in for example U.S. Pat. No.6,372,864 and U.S. Patent Application Publication No. 20060247373A1which are incorporated herein by reference.

Homogeneously branched ethylene copolymers can be prepared using anycatalyst capable of producing homogeneous branching. Generally, thecatalysts will be based on a group 4 metal having at least onecyclopentadienyl ligand that is well known in the art. Examples of suchcatalysts, which include metallocenes, constrained geometry catalystsand phosphinimine catalysts are typically used in combination withactivators selected from methylaluminoxanes, boranes or ionic boratesalts and are further described in U.S. Pat. Nos. 3,645,992; 5,324,800;5,064,802; 5,055,438; 6,689,847; 6,114,481 and 6,063,879. Such catalystsmay also be referred to as “single site catalysts” to distinguish themfrom traditional Ziegler-Natta or Phillips catalysts which are also wellknown in the art. In general, single site catalysts produce ethylenecopolymers having a molecular weight distribution (Mw/M_(n)) of lessthan about 3.0 and a composition distribution breadth index (CDBI⁵⁰) ofgreater than about 50% by weight.

In an embodiment of the current disclosure, homogeneously branchedethylene polymers are prepared using an organometallic complex of agroup 3, 4 or 5 metal that is further characterized as having aphosphinimine ligand. Such catalysts are known generally asphosphinimine catalysts. Some non-limiting examples of phosphiniminecatalysts can be found in U.S. Pat. Nos. 6,342,463; 6,235,672;6,372,864; 6,984,695; 6,063,879; 6,777,509 and 6,277,931 all of whichare incorporated by reference herein.

Some non-limiting examples of metallocene catalysts can be found in U.S.Pat. Nos. 4,808,561; 4,701,432; 4,937,301; 5,324,800; 5,633,394;4,935,397; 6,002,033 and 6,489,413, which are incorporated herein byreference. Some non-limiting examples of constrained geometry catalystscan be found in U.S. Pat. Nos. 5,057,475; 5,096,867; 5,064,802;5,132,380; 5,703,187 and 6,034,021, all of which are incorporated byreference herein in their entirety.

In an embodiment of the disclosure, use of a single site catalyst thatdoes not produce long chain branching (LCB) is preferred. Withoutwishing to be bound by any single theory, long chain branching canincrease viscosity at low shear rates, thereby negatively impactingcycle times during the manufacture of caps and closures, such as duringthe process of compression molding. Long chain branching may bedetermined using ¹³C NMR methods and may be quantitatively assessedusing the method disclosed by Randall in Rev. Macromol. Chem. Phys. 029(2 and 3), p. 285.

In an embodiment of the disclosure, the polyethylene composition willcontain fewer than 0.3 long chain branches per 1000 carbon atoms. Inanother embodiment of the disclosure, the polyethylene composition willcontain fewer than 0.01 long chain branches per 1000 carbon atoms.

In an embodiment of the disclosure, the polyethylene composition(defined as above) is prepared by contacting ethylene and at least onealpha-olefin with a polymerization catalyst under solution phasepolymerization conditions in at least two polymerization reactors (foran example of solution phase polymerization conditions see for exampleU.S. Pat. No. 6,372,864; 6,984,695 and U.S. Patent ApplicationPublication No. 20060247373A1 which are incorporated herein byreference).

In an embodiment of the disclosure, the polyethylene composition isprepared by contacting at least one single site polymerization catalystsystem (comprising at least one single site catalyst and at least oneactivator) with ethylene and a least one comonomer (e.g., a C₃-C₈alpha-olefin) under solution polymerization conditions in at least twopolymerization reactors.

In an embodiment of the disclosure, a group 4 single site catalystsystem, comprising a single site catalyst and an activator, is used in asolution phase dual reactor system to prepare a bimodal polyethylenecomposition by polymerization of ethylene in the presence of analpha-olefin comonomer.

In an embodiment of the disclosure, a group 4 single site catalystsystem, comprising a single site catalyst and an activator, is used in asolution phase dual reactor system to prepare a bimodal polyethylenecomposition by polymerization of ethylene in the presence of 1-octene.

In an embodiment of the disclosure, a group 4 phosphinimine catalystsystem, comprising a phosphinimine catalyst and an activator, is used ina solution phase dual reactor system to prepare a bimodal polyethylenecomposition by polymerization of ethylene in the presence of analpha-olefin comonomer.

In an embodiment of the disclosure, a group 4 phosphinimine catalystsystem, comprising a phosphinimine catalyst and an activator, is used ina solution phase dual reactor system to prepare a bimodal polyethylenecomposition by polymerization of ethylene in the presence of 1-octene.

In an embodiment of the disclosure, a solution phase dual reactor systemcomprises two solution phase reactors connected in series.

In an embodiment of the disclosure, a polymerization process to preparethe polyethylene composition comprises contacting at least one singlesite polymerization catalyst system with ethylene and at least onealpha-olefin comonomer under solution polymerization conditions in atleast two polymerization reactors.

In an embodiment of the disclosure, a polymerization process to preparethe polyethylene composition comprises contacting at least one singlesite polymerization catalyst system with ethylene and at least onealpha-olefin comonomer under solution polymerization conditions in atleast a first reactor and a second reactor configured in series.

In an embodiment of the disclosure, a polymerization process to preparethe polyethylene composition comprises contacting at least one singlesite polymerization catalyst system with ethylene and at least onealpha-olefin comonomer under solution polymerization conditions in atleast a first reactor and a second reactor configured in series, withthe at least one alpha-olefin comonomer being fed exclusively to thefirst reactor.

The production of the polyethylene composition of the present disclosurewill typically include an extrusion or compounding step. Such steps arewell known in the art.

The polyethylene composition can comprise further polymer components inaddition to the first and second ethylene polymers. Such polymercomponents include polymers made in situ or polymers added to thepolymer composition during an extrusion or compounding step.

Optionally, additives can be added to the polyethylene composition.Additives can be added to the polyethylene composition during anextrusion or compounding step, but other suitable known methods will beapparent to a person skilled in the art. The additives can be added asis or as part of a separate polymer component (i.e. not the first orsecond ethylene polymers described above) added during an extrusion orcompounding step. Suitable additives are known in the art and includebut are not-limited to antioxidants, phosphites and phosphonites,nitrones, antacids, UV light stabilizers, UV absorbers, metaldeactivators, dyes, fillers and reinforcing agents, nano-scale organicor inorganic materials, antistatic agents, lubricating agents such ascalcium stearates, slip additives such as erucimide, and nucleatingagents (including nucleators, pigments or any other chemicals which mayprovide a nucleating effect to the polyethylene composition). Theadditives that can be optionally added are typically added in amount ofup to 20 weight percent (wt %).

One or more nucleating agent(s) may be introduced into the polyethylenecomposition by kneading a mixture of the polymer, usually in powder orpellet form, with the nucleating agent, which may be utilized alone orin the form of a concentrate containing further additives such asstabilizers, pigments, antistatics, UV stabilizers and fillers. Itshould be a material which is wetted or absorbed by the polymer, whichis insoluble in the polymer and of melting point higher than that of thepolymer, and it should be homogeneously dispersible in the polymer meltin as fine a form as possible (1 to 10 μm). Compounds known to have anucleating capacity for polyolefins include salts of aliphatic monobasicor dibasic acids or arylalkyl acids, such as sodium succinate, oraluminum phenylacetate; and alkali metal or aluminum salts of aromaticor alicyclic carboxylic acids such as sodium p-naphthoate, or sodiumbenzoate.

Examples of nucleating agents which are commercially available and whichmay be added to the polyethylene composition are dibenzylidene sorbitalesters (such as the products sold under the trademark Millad.™. 3988 byMilliken Chemical and Irgacleamm by Ciba Specialty Chemicals). Furtherexamples of nucleating agents which may be added to the polyethylenecomposition include the cyclic organic structures disclosed in U.S. Pat.No. 5,981,636 (and salts thereof, such as disodium bicyclo [2.2.1]heptene dicarboxylate); the saturated versions of the structuresdisclosed in U.S. Pat. No. 5,981,636 (as disclosed in U.S. Pat. No.6,465,551; Zhao et al., to Milliken); the salts of certain cyclicdicarboxylic acids having a hexahydrophthalic acid structure (or “HHPA”structure) as disclosed in U.S. Pat. No. 6,599,971 (Dotson et al., toMilliken); and phosphate esters, such as those disclosed in U.S. Pat.No. 5,342,868 and those sold under the trade names NA-11 and NA-21 byAsahi Denka Kogyo, cyclic dicarboxylates and the salts thereof, such asthe divalent metal or metalloid salts, (particularly, calcium salts) ofthe HHPA structures disclosed in U.S. Pat. No. 6,599,971. For clarity,the HHPA structure generally comprises a ring structure with six carbonatoms in the ring and two carboxylic acid groups which are substituentson adjacent atoms of the ring structure. The other four carbon atoms inthe ring may be substituted, as disclosed in U.S. Pat. No. 6,599,971. Anexample is 1,2-cyclohexanedicarboxylicacid, calcium salt (CAS registrynumber 491589-22-1). Still further examples of nucleating agents whichmay be added to the polyethylene composition include those disclosed inWO2015042561, WO2015042563, WO2015042562 and WO2011050042.

Many of the above described nucleating agents may be difficult to mixwith the polyethylene composition that is being nucleated and it isknown to use dispersion aids, such as, for example, zinc stearate, tomitigate this problem.

In an embodiment of the disclosure, the nucleating agents are welldispersed in the polyethylene composition.

In an embodiment of the disclosure, the amount of nucleating agent usedis comparatively small—from 100 to 3000 parts by million per weight(based on the weight of the polyethylene composition) so it will beappreciated by those skilled in the art that some care must be taken toensure that the nucleating agent is well dispersed. In an embodiment ofthe disclosure, the nucleating agent is added in finely divided form(less than 50 microns, especially less than 10 microns) to thepolyethylene composition to facilitate mixing. This type of “physicalblend” (i.e., a mixture of the nucleating agent and the resin in solidform) is generally preferable to the use of a “masterbatch” of thenucleator (where the term “masterbatch” refers to the practice of firstmelt mixing the additive—the nucleator, in this case—with a small amountof the polyethylene composition resin—then melt mixing the “masterbatch”with the remaining bulk of the polyethylene composition resin).

In an embodiment of the disclosure, an additive such as nucleating agentmay be added to the polyethylene composition by way of a “masterbatch”,where the term “masterbatch” refers to the practice of first melt mixingthe additive (e.g., a nucleator) with a small amount of the polyethylenecomposition, followed by melt mixing the “masterbatch” with theremaining bulk of the polyethylene composition.

In an embodiment of the disclosure, the polymer composition furthercomprises a nucleating agent or a mixture of nucleating agents.

In an embodiment of the disclosure, the polymer compositions describedabove are used in the formation of molded articles. For example,articles formed by compression molding and injection molding arecontemplated. Such articles include, for example, caps, screw caps, andclosures for bottles and/or containers. However, a person skilled in theart will readily appreciate that the compositions described above mayalso be used for other applications such as but not limited to film,injection blow molding, blow molding and sheet extrusion applications.

In an embodiment of the disclosure, the polyethylene compositionsdescribed above are used in the formation of a closure for bottles,containers, pouches and the like. For example, closures for bottlesformed by compression molding or injection molding are contemplated.Such closures include, for example, hinged caps, hinged screw caps,hinged snap-top caps, and hinged closures for bottles, containers,pouches and the like.

In an embodiment of the disclosure, a closure (or cap) is a screw capfor a bottle, container, pouches and the like.

In an embodiment of the disclosure, a closure (or cap) is a snap closurefor a bottle, container, pouches and the like.

In an embodiment of the disclosure, a closure (or cap) comprises a hingemade of the same material as the rest of the closure (or cap).

In an embodiment of the disclosure, a closure (or cap) is hingedclosure.

In an embodiment of the disclosure, a closure (or cap) is a hingedclosure for bottles, containers, pouches and the like.

In an embodiment of the disclosure, a closure (or cap) is a flip-tophinge closure, such as a flip-top hinge closure for use on a plasticketchup bottle or similar containers containing foodstuffs.

When a closure is a hinged closure, it comprises a hinged component andgenerally consists of at least two bodies which are connected by athinner section that acts as a hinge allowing the at least two bodies tobend from an initially molded position. The thinner section may becontinuous or web-like, wide or narrow.

A useful closure (for bottles, containers and the like) is a hingedclosure and may consist of two bodies joined to each other by at leastone thinner bendable portion (e.g. the two bodies can be joined by asingle bridging portion, or more than one bridging portion, or by awebbed portion, etc.). A first body may contain a dispensing hole andwhich may snap onto or screw onto a container to cover a containeropening (e.g. a bottle opening) while a second body may serve as a snapon lid which may mate with the first body.

The caps and closures, of which hinged caps and closures and screw capsetc. are a subset, can be made according to any known method, includingfor example injection molding and compression molding techniques thatare well known to persons skilled in the art. Hence, in an embodiment ofthe disclosure a closure (or cap) comprising the polyethylenecomposition (defined above) is prepared with a process comprising atleast one compression molding step and/or at least one injection moldingstep.

In one embodiment, the caps and closures (including single piece ormulti-piece variants or hinged variants) comprise the polyethylenecomposition described above and have good organoleptic properties, goodtoughness, as well as good ESCR values. Hence the closures and caps ofthis embodiment are well suited for sealing bottles, containers and thelike, for examples bottles that may contain drinkable water, and otherfoodstuffs, including but not limited to liquids that are under anappropriate pressure (i.e., carbonated beverages or appropriatelypressurized drinkable liquids).

The closures and caps may also be used for sealing bottles containingdrinkable water or non-carbonated beverages (e.g., juice). Otherapplications, include caps and closures for bottles, containers andpouches containing foodstuffs, such as for example ketchup bottles andthe like.

The disclosure is further illustrated by the following non-limitingexamples.

EXAMPLES

M_(n), M_(w), and M_(z) (g/mol) were determined by high temperature GelPermeation Chromatography (GPC) with differential refractive index (DRI)detection using universal calibration (e.g. ASTM 06474-99). GPC data wasobtained using an instrument sold under the trade name “Waters 150c”,with 1,2,4-trichlorobenzene as the mobile phase at 140° C. The sampleswere prepared by dissolving the polymer in this solvent and were runwithout filtration. Molecular weights are expressed as polyethyleneequivalents with a relative standard deviation of 2.9% for the numberaverage molecular weight (“Mn”) and 5.0% for the weight averagemolecular weight (“Mw”). The molecular weight distribution (MWD) is theweight average molecular weight divided by the number average molecularweight, Mw/M_(n). The z-average molecular weight distribution isM_(z)/M_(n). Polymer sample solutions (1 to 2 mg/mL) were prepared byheating the polymer in 1,2,4-trichlorobenzene (TCB) and rotating on awheel for 4 hours at 150° C. in an oven. The antioxidant2,6-di-tert-butyl-4-methylphenol (BHT) was added to the mixture in orderto stabilize the polymer against oxidative degradation. The BHTconcentration was 250 ppm. Sample solutions were chromatographed at 140°C. on a PL 220 high-temperature chromatography unit equipped with fourShodex columns (HT803, HT804, HT805 and HT806) using TCB as the mobilephase with a flow rate of 1.0 mL/minute, with a differential refractiveindex (DRI) as the concentration detector. BHT was added to the mobilephase at a concentration of 250 ppm to protect the columns fromoxidative degradation. The sample injection volume was 200 mL. The rawdata were processed with Cirrus GPC software. The columns werecalibrated with narrow distribution polystyrene standards. Thepolystyrene molecular weights were converted to polyethylene molecularweights using the Mark-Houwink equation, as described in the ASTMstandard test method D6474.

Primary melting peak (° C.), heat of fusion (J/g) and crystallinity (%)was determined using differential scanning calorimetry (DSC) as follows:the instrument was first calibrated with indium; after the calibration,a polymer specimen is equilibrated at 0° C. and then the temperature wasincreased to 200° C. at a heating rate of 10° C./min; the melt was thenkept isothermally at 200° C. for five minutes; the melt was then cooledto 0° C. at a cooling rate of 10° C./min and kept at 0° C. for fiveminutes; the specimen was then heated to 200° C. at a heating rate of10° C./min. The DSC Tm, heat of fusion and crystallinity are reportedfrom the 2^(nd) heating cycle.

The short chain branch frequency (SCB per 1000 carbon atoms) ofcopolymer samples was determined by Fourier Transform InfraredSpectroscopy (FTIR) as per the ASTM D6645-01 method. A Thermo-Nicolet750 Magna-IR Spectrophotometer equipped with OMNIC version 7.2a softwarewas used for the measurements.

Comonomer content can also be measured using ¹³C NMR techniques asdiscussed in Randall, Rev. Macromol. Chem. Phys., C29 (2&3), p 285; U.S.Pat. No. 5,292,845 and WO 2005/121239.

Polyethylene composition density (g/cm³) was measured according to ASTMD792.

Hexane extractables were determined according to ASTM D5227.

Shear viscosity was measured by using a Kayeness WinKARS CapillaryRheometer (model # D5052M-115). For the shear viscosity at lower shearrates, a die having a die diameter of 0.06 inch and L/D ratio of 20 andan entrance angle of 180 degrees was used. For the shear viscosity athigher shear rates, a die having a die diameter of 0.012 inch and L/Dratio of 20 was used.

The Shear Viscosity Ratio as the term is used in the present disclosureis defined as: η₁₀/η₁₀₀₀ at 240° C. The η₁₀ is the melt shear viscosityat the shear rate of 10 s⁻¹ and the η₁₀₀₀ is the melt shear viscosity atthe shear rate of 1000 s⁻¹ measured at 240° C.

Melt indexes, I₂, I₅, I₆ and I₂₁ for the polyethylene composition weremeasured according to ASTM D1238 (when conducted at 190° C., using a2.16 kg, a 5 kg, a 6.48 kg and a 21 kg weight respectively).

The “Rosand” melt strength of the polyethylene composition was measuredon Rosand RH-7 capillary rheometer (barrel diameter=15 mm) with a flatdie of 2-mm Diameter, L/D ratio 10:1 at 190° C. Pressure Transducer:10,000 psi (68.95 MPa). Piston Speed: 5.33 mm/min. Haul-off Angle: 52°.Haul-off incremental speed: 50-80 m/min² or 65±15 m/min². A polymer meltis extruded through a capillary die under a constant rate and then thepolymer strand is drawn at an increasing haul-off speed until itruptures. The maximum steady value of the force in the plateau region ofa force versus time curve is defined as the melt strength for thepolymer.

To determine CDBI₅₀, a solubility distribution curve is first generatedfor the polyethylene composition. This is accomplished using dataacquired from the TREF technique. This solubility distribution curve isa plot of the weight fraction of the copolymer that is solubilized as afunction of temperature. This is converted to a cumulative distributioncurve of weight fraction versus comonomer content, from which the CDBI₅₀is determined by establishing the weight percentage of a copolymersample that has a comonomer content within 50% of the median comonomercontent on each side of the median (See WO 93/03093 and U.S. Pat. No.5,376,439). The CDBI₂₅ is determined by establishing the weightpercentage of a copolymer sample that has a comonomer content within 25%of the median comonomer content on each side of the median.

The specific temperature rising elution fractionation (TREF) method usedherein was as follows. Polymer samples (50 to 150 mg) were introducedinto the reactor vessel of a crystallization-TREF unit (Polymer ChAR™).The reactor vessel was filled with 20 to 40 ml 1,2,4-trichlorobenzene(TCB), and heated td the desired dissolution temperature (e.g., 150° C.)for Ito 3 hours. The solution (0.5 to 1.5 ml) was then loaded into theTREF column filled with stainless steel beads. After equilibration at agiven stabilization temperature (e.g., 110° C.) for 30 to 45 minutes,the polymer solution was allowed to crystallize with a temperature dropfrom the stabilization temperature to 30° C. (0.1 or 0.2° C./minute).After equilibrating at 30° C. for 30 minutes, the crystallized samplewas eluted with TCB (0.5 or 0.75 mL/minute) with a temperature ramp from30° C. to the stabilization temperature (0.25 or 1.0° C./minute). TheTREF column was cleaned at the end of the run for 30 minutes at thedissolution temperature. The data were processed using Polymer ChARsoftware, Excel spreadsheet and TREF software developed in-house.

The melt index, I₂ and density of the first and second ethylenecopolymers were estimated by GPC and GPC-FTIR deconvolutions asdiscussed further below.

High temperature GPC equipped with an online FTIR detector (GPC-FTIR)was used to measure the comonomer content as the function of molecularweight. Mathematical deconvolutions are performed to determine therelative amount of polymer, molecular weight and comonomer content ofthe component made in each reactor, by assuming that each polymercomponent follows a Flory's molecular weight distribution function andit has a homogeneous comonomer distribution across the whole molecularweight range.

For these single site catalyzed resins, the GPC data from GPCchromatographs was fit based on Flory's molecular weight distributionfunction.

To improve the deconvolution accuracy and consistency, as a constraint,the melt index, I₂, of the targeted resin was set and the followingrelationship was satisfied during the deconvolution:

Log₁₀(I₂)=22.326528+0.003467*[Log₁₀(M_(n))]³−4.322582*Log₁₀(M_(w))−0.180061*[Log₁₀(M_(z))]²+0.026478*[Log₁₀(M_(z))]³

where the experimentally measured overall melt index, I₂, was used onthe left side of the equation, while M_(n) of each component(M_(w)=2×M_(n) and M_(z)=1.5×M_(w) for each component) was adjusted tochange the calculated overall M_(n), M_(w) and M_(z) of the compositionuntil the fitting criteria were met. During the deconvolution, theoverall M_(n), M_(w) and M_(z) are calculated with the followingrelationships: M_(n)=1/SUM(w_(i)/M_(n)(i)), M_(w)=SUM(w_(i)×M_(w)(i)),M_(z)=SUM(w_(i)×M_(z)(i)²), where i represents the i-th component andw_(i) represents the relative weight fraction of the i-th component inthe composition.

The uniform comonomer distribution (which results from the use of asingle site catalyst) of the resin components (i.e., the first andsecond ethylene copolymers) allowed the estimation of the short chainbranching content (SC B) from the GPC-FTIR data, in branches per 1000carbon atoms and calculation of comonomer content (in mol %) and density(in g/cm³) for the first and second ethylene copolymers, based on thedeconvoluted relative amounts of first and second ethylene copolymercomponents in the polyethylene composition, and their estimated resinmolecular weight parameters from the above procedure.

A component (or composition) density model and a component (orcomposition) melt index, I₂, model was used according to the followingequations to calculate the density and melt index I₂ of the first andsecond ethylene polymers:

density=0.979863−0.00594808*(FTIR SCB/1000C)^(0.65)−0.000383133*[Log₁₀(M_(n))]³0.00000577986*(M_(w)/M_(n))³+0.00557395*(M_(z)/M_(w))^(0.25);

Log₁₀(melt index,I₂)=22.326528+0.003467*[Log₁₀(M_(n))]³−4.322582*Log₁₀(M_(w))−0.180061*[Log₁₀(M_(z))]²+0.026478*[Log₁₀(M_(z))]³

where the M_(n), M_(w) and M_(z) were the deconvoluted values of theindividual ethylene polymer components, as obtained from the results ofthe above GPC deconvolutions. Hence, these two models were used toestimate the melt indexes and the densities of the components (i.e., thefirst and second ethylene copolymers).

Plaques molded from the polyethylene compositions were tested accordingto the following ASTM methods: Bent Strip Environmental Stress CrackResistance (ESCR) at Condition B at 10% IGEPAL at 50° C., ASTM D1693;notched Izod impact properties, ASTM 0256; Flexural Properties, ASTM D790; Tensile properties, ASTM D 638; Vicat softening point, ASTM D 1525;Heat deflection temperature, ASTM D 648.

Dynamic mechanical analyses were carried out with a rheometer, namelyRheometrics Dynamic Spectrometer (RDS-II) or Rheometrics SR5 or ATSStresstech, on compression molded samples under nitrogen atmosphere at190° C., using 25 mm diameter cone and plate geometry. The oscillatoryshear experiments were done within the linear viscoelastic range ofstrain (10% strain) at frequencies from 0.05 to 100 rad/s. The values ofstorage modulus (G′), loss modulus (G″), complex modulus (G*) andcomplex viscosity (η*) were obtained as a function of frequency. Thesame rheological data can also be obtained by using a 25 mm diameterparallel plate geometry at 190° C. under nitrogen atmosphere. The SHI(1,100) value is calculated according to the methods described in WO2006/048253 and WO 2006/048254.

Examples of the polyethylene compositions were produced in a dualreactor solution polymerization process in which the contents of thefirst reactor flow into the second reactor. This in-series “dualreactor” process produces an “in-situ” polyethylene blend (i.e. thepolyethylene composition). Note, that when an in-series reactorconfiguration is used, un-reacted ethylene monomer, and un-reactedalpha-olefin comonomer present in the first reactor will flow into thedownstream second reactor for further polymerization.

In the present inventive examples, although no co-monomer is feddirectly to the downstream second reactor, an ethylene copolymer isnevertheless formed in the second reactor due to the significantpresence of un-reacted 1-octene flowing from the first reactor to thesecond reactor where it is copolymerized with ethylene. Each reactor issufficiently agitated to give conditions in which components are wellmixed. The volume of the first reactor was 12 liters and the volume ofthe second reactor was 22 liters. Optionally, a tubular reactor sectionwhich receives the discharge from the second reactor may be also bepresent as described in U.S. Pat. No. 8,101,693. These are the pilotplant scales. The first reactor was operated at a pressure of 6000 to35000 kPa and the second reactor was operated at a lower pressure tofacilitate continuous flow from the first reactor to the second. Thesolvent employed was methylpentane. The process operates usingcontinuous feed streams. The catalyst employed in the dual reactorsolution process experiments was a titanium complex having aphosphinimine ligand, a cyclopentadienide ligand and two activatableligands, such as but not limited to chloride ligands. A boron basedco-catalyst was used in approximately stoichiometric amounts relative tothe titanium complex. Commercially available methylaluminoxane (MAO) wasincluded as a scavenger at an Al:Ti of about 40:1. In addition,2,6-di-tert-butylhydroxy-4-ethylbenzene was added to scavenge freetrimethylaluminum within the MAO in a ratio of Al:OH of about 0.5:1.

The polymerization conditions used to make the inventive compositionsare provided in Table 1.

Inventive and comparative polyethylene composition properties aredescribed in Table 2.

Calculated properties for the first ethylene copolymer and the secondethylene copolymer for inventive polyethylene compositions, as obtainedfrom GPC-FTIR deconvolution studies, are provided in Table 3.

Comparative polyethylene composition 1 was made using a single sitephosphinimine catalyst in a dual reactor solution process and has anESCR at condition B10 (at 50° C., 10% IGEPAL) of less than 24 hours, aSCB1/SCB2 ratio of 0.50 or less, and a Mz of less than 400,000.

Comparative polyethylene compositions 2 and 3 were made using a singlesite phosphinimine catalyst in a dual reactor solution process and havean ESCR at condition B10 (at 50° C., 10% IGEPAL) of 309 hrs and 86 hrsrespectively, a SCB1/SCB2 ratio of greater than 1.0, and a Mz of lessthan 400,000.

Comparative polyethylene composition 4 is a commercially available, highdensity, bimodal polyethylene resin from Dow Chemical, DMDA-1250 NT 7which has an ESCR at condition B-10 (at 50° C., 10% IGEPAL) of more than150 hours, a melt strength of less than 3.0 cN, and an Mz of greaterthan 500,000. It also has a stress exponent value of 1.58.

Comparative polyethylene composition 5 is a commercially available, highdensity polyethylene resin from Dow Chemical, DMDC-1270 NT 7 which hasan ESCR at condition B-10 (at 50° C., 10% IGEPAL) of less than 100hours, a Rosand melt strength of less than 2.0 cN, and an Mz of greaterthan 450,000. It also has a stress exponent value of 1.53.

Inventive polyethylene compositions (Inventive Examples 1-3) are madeusing a single site phosphinimine catalyst in a dual reactor solutionprocess as described above and have an ESCR at condition B10 (at 50° C.,10% IGEPAL) of greater than 100 hours and a SCB1/SCB2 ratio of greaterthan 1.0. These inventive examples also each have a Mz value of between400,000 and 500,000 and a stress exponent of less than 1.53.

As shown in FIG. 1, inventive polyethylene compositions 1-3 provide animproved balance of ESCR and stiffness (as indicated by 2% secant floralmodulus) when compared to comparative polyethylene compositions 4 and 5.

As shown in FIG. 2, inventive polyethylene compositions 1-3 provide animproved balance of processability (as indicated by the “shear viscosityratio”) and ESCR when compared to comparative polyethylene compositions2, 4 and 5.

FIG. 3 shows that inventive polyethylene compositions 1-3 have animproved balance of processability (as indicated by the “shear viscosityratio”) and melt strength (the Rosand melt strength) when compared tocomparative polyethylene compositions 2, 4 and 5.

FIG. 4 shows the bimodal nature of the inventive polyethylenecompositions 1-3. Each ethylene copolymer component has a M_(w)/M_(n)value of less than 2.5.

As shown in FIG. 5, the inventive polyethylene compositions 1-3 do notsatisfy the equation SHI(_(1,100))≧−10/58 (log I₂ of the polyethylenecomposition in g/10 min)/(g/10 min)+12.94, which is a property of theblends taught in WO 2006/048253. As shown in FIG. 5, the inventivepolyethylene compositions 1-3 do not satisfy the equation:SHI(_(1,100))≧−5.5 (log I₂ of the polyethylene composition in g/10min)/(g/10 min)+9.66, which is a property of the blends taught in and WO2006/048254.

TABLE 1 Reactor Conditions for Inventive Examples Example No. Inventive1 Inventive 2 Inventive 3 Reactor 1 Ethylene (kg/h) 35.4 34.9 36.41-Octene (kg/h) 3.4 4.5 3.6 Hydrogen (g/h) 0.3 0.4 0.5 Solvent (kg/h)353.4 321.8 341 Reactor Feed Inlet 35 35.1 30 Temperature (° C.) ReactorTemperature (° C.) 140 140.7 140 Titanium Catalyst to the 0.093 0.0520.070 Reactor (ppm) Reactor 2 Ethylene (kg/h) 43.3 42.7 44.5 1-Octene(kg/h) 0 0 0 Hydrogen (g/h) 15 17 16 Solvent (kg/h) 104.4 136.2 114.2Reactor Feed Inlet 36.8 36.3 30.3 Temperature (° C.) Reactor Temperature(° C.) 199.9 198.3 201 Titanium Catalyst to the 0.40 0.42 0.52 Reactor(ppm)

TABLE 2 Resin Properties Example No. Inventive 1 Inventive 2 Inventive 3Density (g/cm³) 0.9523 0.953 0.9539 Rheology/Flow Properties Melt IndexI₂ (g/10 0.73 0.77 0.75 min) Melt Flow Ratio 66 85 80.4 (I₂₁/I₂) I₂₁47.9 65 60 I₅ 2.46 I₂₁/I₅ 24.39 Stress Exponent 1.41 1.46 1.46 ShearViscosity at 6.1 5.6 5.2 10⁵ s⁻¹ (240° C., Pa-s) Shear Viscosity 19.919.44 20.9 Ratio η(10s⁻¹)/ η(1000 s⁻¹) at 240° C. Rosand Melt 3.77 3.323.32 Strength (190° C., cN) GPC-conventional M_(n) 15401 13272 13077M_(w) 122538 122190 117899 M_(z) 419614 471630 439444 PolydispersityIndex 7.96 9.21 9.02 (M_(w)/M_(n)) M_(z)/M_(w) 3.42 3.86 3.73 BroadnessFactor 2.33 2.39 2.42 (M_(w)/M_(n))/(M_(z)/M_(w)) Branch Frequency-FTIR(uncorrected for chain end —CH₃) Uncorrected 2.3 2.4 2.3 SCB/1000 CUncorrected 0.5 0.5 0.5 comonomer content (mol %) Internal unsaturation0.05 0.04 0.05 (/1000 C) Side chain 0 0 0 unsaturation (/1000 C)Terminal 0.10 0.09 0.14 unsaturation (/1000 C) Comonomer ID 1-octene1-octene 1-octene Comononner mol % measured by ¹³C-NMR 1-Octene or1-hexene, mol % CDBI₅₀ (wt. %) 75.4 71.9 72.2 CDBI₂₅ (wt. %) 65.4 61.861.8 DSC Primary Melting 128.76 128.63 129.23 Peak (° C.) Heat of Fusion(J/g) 215.3 217.8 220.4 Crystallinity (%) 74.23 75.11 76 EnvironmentalStress Crack Resistance (Plaques) ESCR Cond. B at 10 365 310 227 % (hrs)Flexural Properties (Plaques) Flex Secant Mod. 1264 1281 1303 1% (MPa)Flex Sec Mod 1% 20 12 32 (MPa) Dev. Flex Secant Mod. 1054 1075 1090 2%(MPa) Flex Sec Mod 2% 14 16 24 (MPa) Dev. Flexural Strength 36.6 37.437.6 (MPa) Flexural Strength 0.4 0.5 0.5 Dev. (MPa) Tensile Properties(Plaques) Elong. at Yield (%) 10 9 9 Elong. at Yield Dev. 1 1 0 (%)Yield Strength (MPa) 26.1 26.9 26.9 Yield Strength Dev. 0.4 0.5 0.6(MPa) Ultimate Elong. (%) 781 710 877 Ultimate Elong. Dev. 77 45 106 (%)Ultimate Strength 29.7 19.3 28.6 (MPa) Ultimate Strength 7 3.8 5.6 Dev.(MPa) Sec Mod 1% (MPa) 1380 1672 1470 Sec Mod 1% (MPa) 294 322 177 Dev.Sec Mod 2% (MPa) 913 1034 978 Sec Mod 2% (MPa) 80 95 64 Dev. ImpactProperties (Plaques) Izod Impact (J/m) 106.8 80.0 85.4 IZOD DV (J/m) 0.05.3 0.0 Other properties Hexane Extractables 0.38 0.38 0.39 (%) VICATSoft. Pt. (° C.)- 126.2 126.5 126.5 Plaque Heat Deflection 65.5 72.769.3 Temp. [° C.] @ 66 PSI Comparative Comparative ComparativeComparative Comparative Example No. 1 2 3 4 5 Density (g/cm³) 0.95340.9529 0.9523 0.955 0.955 Rheology/Flow Properties Melt Index I₂ (g/10min) 1.88 1.57 1.5 1.5 2.5 Melt Flow Ratio (I₂₁/I₂) 56.9 58 54.8 66 51I₂₁ 90 82.3 99 113 I₅ 4.72 4.5 5.31 7.8 I₂₁/I₅ 19.07 18.29 18.64 14.49Stress Exponent 1.41 1.38 1.4 1.58 1.53 Shear Viscosity at 10⁵ s⁻¹ 5.16.2 6.63 (240° C., Pa-s) Shear Viscosity Ratio 13.5 11.3 9.48 η(10s⁻¹)/η(1000 s⁻¹) at 240° C. Rosand Melt Strength 2.12 2.56 1.79 (190°C., cN) GPC-conventional M_(n) 14393 10524 13309 10240 17100 M_(w) 9166383712 88295 106992 102000 M_(z) 245479 256210 278141 533971 470400Polydispersity Index 6.37 7.95 6.63 10.45 5.96 (M_(w)/M_(n)) M_(z)/M_(w)2.68 3.06 3.15 4.99 4.61 Broadness Factor 2.8 2.60 2.11 2.09 1.20(M_(w)/M_(n))/(M_(z)/M_(w)) Branch Frequency-FTIR (uncorrected for chainend —CH₃) Uncorrected SCB/1000 C 2.2 3 2.1 2.3 2.5 Uncorrected comonomer0.4 0.6 0.4 0.5 0.5 content (mol %) Internal unsaturation 0 0 (/1000 C)Side chain unsaturation 0.09 0 (/1000 C) Terminal unsaturation 0.13 0.17(/1000 C) Comonomer ID 1-octene 1-octene 1-octene 1-hexene 1-hexeneComonomer mol % measured by ¹³C-NMR 1-Octene or 1-hexene, mol % 0.3 0.68CDBI₅₀ (wt. %) 36.7 81.8 76.5 63.4 67.3 CDBI₂₅ (wt. %) 17.6 39 49.8 DSCPrimary Melting Peak (° C.) 128.3 127.3 129 130.06 131.24 Heat of Fusion(J/g) 204.7 203.8 209.00 217.4 217.6 Crystallinity (%) 70.58 70.27 72.0874.98 75.04 Environmental Stress Crack Resistance (Plaque) ESCR Cond. Bat 10% (hrs) <24 309 86 196 78 Flexural Properties (Plaques) Flex SecantMod. 1% (MPa) 1035 1274 1295 1372 1304 Flex Sec Mod 1% (MPa) Dev. 25 3923 87 46 Flex Secant Mod. 2% (MPa) 877 1064 1085 1167 1102 Flex Sec Mod2% (MPa) Dev. 19 29 21 45 41 Flexural Strength (MPa) 31.5 37.5 37.3 40.438.3 Flexural Strength Dev. (MPa) 0.6 0.8 0.4 1 0.6 Tensile Properties(Plaques) Elong. at Yield (%) 10.2 9 10 9 9 Elong. at Yield Dev. (%) 0.81 0 1 1 Yield Strength (MPa) 26.6 26 26.3 28.5 26.4 Yield Strength Dev.(MPa) 0.3 0.2 0.3 0.3 0.3 Ultimate Elong. (%) 920 701 891 870 1055Ultimate Elong. Dev. (%) 94.6 106 23 69 42 Ultimate Strength (MPa) 21.521.8 33.3 26.8 31.6 Ultimate Strength Dev. (MPa) 4.1 6.8 2 5.5 1 Sec Mod1% (MPa) 1374 1483 1230 1696 1545 Sec Mod 1% (MPa) Dev. 276.4 121 90 279231 Sec Mod 2% (MPa) 937 973 913 1118 993 Sec Mod 2% (MPa) Dev. 71 33 3490 91 Impact Properties (Plaques) lzod Impact (J/m) 76.0 74.7 80.1 80.180.0 IZOD DV (J/m) 7.0 0.0 2.7 5.3 Other properties Hexane Extractables(%) 0.44 0.36 0.25 0.36 0.48 VICAT Soft. Pt. (° C.)-Plaque 126 125.2126.4 126.8 126.6 Heat Deflection Temp. 72 68 67.3 73 76.4 [° C.] @ 66PSI

TABLE 3 Polyethylene Component Properties Example No. Comparative 1Comparative 3 Inventive 1 Inventive 2 Inventive 3 Density (g/cm³) 0.95340.9523 0.9523 0.953 0.9539 I2 (g/10 min.) 1.88 1.5 0.73 0.77 0.75 StressExponent 1.41 1.4 1.41 1.46 1.46 MFR (I₂₁/I₂) 56.9 54.8 66 85 80.4 M_(n)14393 13309 15401 13272 13077 M_(w) 91663 88295 122538 122190 117899M_(z) 245479 278141 419614 471630 439444 400000 < M_(z) < 520000 no noyes yes yes M_(w)/M_(n) 6.37 6.63 7.96 9.21 9.02 M_(z)/M_(w) 2.68 3.153.42 3.86 3.73 First Ethylene Copolymer weight % 0.43 0.454 0.447 0.4190.421 Mw 162400 168100 209700 221100 221400 I₂ (g/10 min.) 0.13 0.120.05 0.04 0.04 Density 1, d₁ (g/cm³) 0.9389 0.9302 0.9332 0.9333 0.9339SCB1 per 1000 Cs 0.15 2.24 0.6 0.45 0.34 Second Ethylene Copolymerweight % 0.57 0.546 0.553 0.581 0.579 Mw 18500 14900 14600 13600 13800I₂ (g/10 min.) 736 1817 1981 2696 2515 Density 2, d₂ (g/cm³) 0.95590.9555 0.9618 0.9626 0.9622 SCB1 per 1000 Cs 1.06 1.64 0.2 0.17 0.2Estimated (d₂ − d₁), 0.017 0.0253 0.0286 0.0293 0.0283 g/cm³ Estimated(SCB2 − 0.91 −0.6 −0.4 −0.28 −0.14 SCB1) SCB1/SCB2 0.16 1.37 3.00 2.651.70

What is claimed is:
 1. A closure, said closure comprising a bimodalpolyethylene composition comprising: (1) 10 to 70 wt % of a firstethylene copolymer having a melt index I₂, of less than 0.4 g/10 min; amolecular weight distribution M_(w)/M_(n), of less than 2.7; and adensity of from 0.920 to 0.955 g/cm³; and (2) 90 to 30 wt % of a secondethylene copolymer having a melt index I₂, of from 250 to 20,000 g/10min; a molecular weight distribution M_(w)/M_(n), of less than 2.7; anda density higher than the density of said first ethylene copolymer, butless than 0.965 g/cm³; wherein the density of said second ethylenecopolymer is less than 0.035 g/cm³ higher than the density of said firstethylene copolymer; the ratio (SCB1/SCB2) of the number of short chainbranches per thousand carbon atoms in said first ethylene copolymer(SCB1) to the number of short chain branches per thousand carbon atomsin said second ethylene copolymer (SCB2) is greater than 1.0; andwherein said bimodal polyethylene composition has a molecular weightdistribution M_(w)/M_(n), of from 5.0 to 13.0, a density of from 0.949to 0.958 9/cm³, a stress exponent of less than 1.53, a melt index (I₂)of from 0.3 to 3.0 g/10 min, and which satisfies the following:400,000≦Mz≦500,000.
 2. The closure of claim 1 wherein said bimodalpolyethylene composition has an ESCR Condition B (10% IGEPAL) of atleast 150 hrs.
 3. The closure of claim 1 wherein said bimodalpolyethylene composition has a molecular weight distribution,M_(w)/M_(n), of from 6.0 to 12.0.
 4. The closure of claim 1 wherein saidbimodal polyethylene composition has melt index I₂, of from about 0.3 toabout 1.0 g/10 min.
 5. The closure of claim 1 wherein said bimodalpolyethylene composition has a density of from 0.951 to 0.957 g/cm³. 6.The closure of claim 1 wherein said second ethylene copolymer has a meltindex I₂, of greater than 500 g/10 min.
 7. The closure of claim 1wherein said first and second ethylene copolymers have a M_(w)/M_(n) ofless than 2.5.
 8. The closure of claim 1 wherein said bimodalpolyethylene composition has a composition distribution breadth index(CDBI₂₅) of greater than 55% by weight.
 9. The closure of claim 1wherein said bimodal polyethylene composition comprises: from 30 to 60wt % of said first ethylene copolymer; and from 70 to 40 wt % of saidsecond ethylene copolymer.
 10. The closure of claim 1 wherein saidbimodal polyethylene composition has a Rosand melt strength of at least3.0 cN.
 11. The closure of claim 1 wherein said bimodal polyethylenecomposition has a broadness factor defined as(M_(w)/M_(n))/(M_(z)/M_(w)) of ≦2.75.
 12. The closure of claim 1 whereinsaid bimodal polyethylene composition has a shear viscosity ratio ofgreater than or equal to
 15. 13. The closure of claim 2 wherein saidbimodal polyethylene composition has a shear viscosity ratio of greaterthan or equal to
 15. 14. The closure of claim 10 wherein said bimodalpolyethylene composition has a shear viscosity ratio of greater than orequal to
 15. 15. The closure of claim 1 wherein the bimodal polyethylenecomposition further comprises a nucleating agent or a mixture ofnucleating agents.
 16. The closure of claim 1 wherein said first andsecond ethylene copolymers are copolymers of ethylene and 1-octene. 17.The closure of claim 1 wherein said closure is made by compressionmolding or injection molding.
 18. A process to prepare a polyethylenecomposition, said polyethylene composition comprising: (1) 10 to 70 wt %of a first ethylene copolymer having a melt index I₂, of less than 0.4g/10 min; a molecular weight distribution M_(w)/M_(n), of less than 2.7;and a density of from 0.920 to 0.955 g/cm³; and (2) 90 to 30 wt % of asecond ethylene copolymer having a melt index I₂, of from 250 to 20,000g/10 min; a molecular weight distribution M_(w)/M_(n), of less than 2.7;and a density higher than the density of said first ethylene copolymer,but less than 0.965 g/cm³; wherein the density of said second ethylenecopolymer is less than 0.035 g/cm³ higher than the density of said firstethylene copolymer; the ratio (SCB1/SCB2) of the number of short chainbranches per thousand carbon atoms in said first ethylene copolymer(SCB1) to the number of short chain branches per thousand carbon atomsin said second ethylene copolymer (SCB2) is greater than 1.0; andwherein said bimodal polyethylene composition has a molecular weightdistribution M_(w)/M_(n), of from 5.0 to 13.0, a density of from 0.949to 0.958 g/cm³, a stress exponent of less than 1.53, a melt index (I₂)of from 0.3 to 3.0 g/10 min, a broadness factor defined as(M_(w)/M_(n))/(M_(z)/M_(w)) of 5 2.75, and which satisfies thefollowing: 400,000≦Mz≦500,000; said process comprising contacting atleast one single site polymerization catalyst system with ethylene andat least one alpha-olefin under solution polymerization conditions in atleast two polymerization reactors.
 19. The process of claim 18 whereinsaid at least two polymerization reactors comprise a first reactor and asecond reactor configured in series.
 20. The process of claim 18 whereinsaid at least two polymerization reactors comprise a first reactor and asecond reactor configured in parallel.
 21. The process of claim 19wherein said at least one alpha-olefin is feed exclusively to said firstreactor.
 22. A bimodal polyethylene composition comprising: (1) 10 to 70wt % of a first ethylene copolymer having a melt index I₂, of less than0.4 g/10 min; a molecular weight distribution M_(w)/M_(n), of less than2.7; and a density of from 0.920 to 0.955 g/cm³; and (2) 90 to 30 wt %of a second ethylene copolymer having a melt index I₂, of from 250 to20,000 g/10 min; a molecular weight distribution M_(w)/M_(n), of lessthan 2.7; and a density higher than the density of said first ethylenecopolymer, but less than 0.965 g/cm³; wherein the density of said secondethylene copolymer is less than 0.035 g/cm³ higher than the density ofsaid first ethylene copolymer; the ratio (SCB1/SCB2) of the number ofshort chain branches per thousand carbon atoms in said first ethylenecopolymer (SCB1) to the number of short chain branches per thousandcarbon atoms in said second ethylene copolymer (SCB2) is greater than1.0; and wherein said bimodal polyethylene composition has a molecularweight distribution M_(w)/M_(n), of from 5.0 to 13.0, a density of from0.949 to 0.958 g/cm³, a stress exponent of less than 1.53, a melt index(I₂) of from 0.3 to 3.0 g/10 min, and which satisfies the following:400,000≦Mz≦500,000.
 23. The bimodal polyethylene composition of claim 22wherein said bimodal polyethylene composition has an ESCR Condition B(10% IGEPAL) of at least 150 hrs.
 24. The bimodal polyethylenecomposition of claim 22 wherein said bimodal polyethylene compositionhas a molecular weight distribution, M_(w)/M_(n), of from 6.0 to
 12. 25.The bimodal polyethylene composition of claim 22 wherein said bimodalpolyethylene composition has a melt index I₂, of from 0.3 to less than1.0 g/10 min.
 26. The bimodal polyethylene composition of claim 22wherein said bimodal polyethylene composition has a density of from0.951 to 0.957 g/cm³.
 27. The bimodal polyethylene composition of claim22 wherein said second ethylene copolymer has a melt index I₂, ofgreater than 500 g/10 min.
 28. The bimodal polyethylene composition ofclaim 22 wherein said first and second ethylene copolymers have aM_(w)/M_(n) of less than 2.5.
 29. The bimodal polyethylene compositionof claim 22 wherein said bimodal polyethylene composition has acomposition distribution breadth index (CDBI₂₅) of greater than 55% byweight.
 30. The bimodal polyethylene composition of claim 22 whereinsaid bimodal polyethylene composition comprises: from 30 to 60 wt % ofsaid first ethylene copolymer; and from 70 to 40 wt % of said secondethylene copolymer.
 31. The bimodal polyethylene composition of claim 22wherein said bimodal polyethylene composition has a Rosand melt strengthof at least 3.0 cN
 32. The bimodal polyethylene composition of claim 22wherein said bimodal polyethylene composition has a broadness factordefined as (M_(w)/M_(n))/(M_(z)/M_(w)) of ≦2.75.
 33. The bimodalpolyethylene composition of claim 22 wherein said bimodal polyethylenecomposition has a shear viscosity ratio of ≧15.
 34. The bimodalpolyethylene composition of claim 23 wherein said bimodal polyethylenecomposition has a shear viscosity ratio of ≧15.
 35. The bimodalpolyethylene composition of claim 31 wherein said bimodal polyethylenecomposition has a shear viscosity ratio of ≧15.